Dipole ring magnet assisted microwave radial line slot antenna plasma processing method and apparatus

ABSTRACT

A method and apparatus is provided for obtaining a low average electron energy flux onto a substrate in a processing chamber. A processing chamber includes a substrate support therein for chemical processing. An energy source induced plasma, and ion propelling means, directs energetic plasma electrons toward the substrate support. A dipole ring magnet field is applied perpendicular to the direction of ion travel, to effectively prevent electrons above an acceptable maximum energy level from reaching the substrate holder. Rotation of the dipole magnetic field reduces electron non-uniformities.

CROSS REFERENCE TO RELATED APPLICATION

Pursuant to 37 C.F.R. §1.78(a)(4), the present application claims thebenefit of and priority to co-pending Provisional Application No.62/142,868 filed on Apr. 3, 2015, and entitled DIPOLE RING MAGNETASSISTED MICROWAVE RADIAL LINE SLOT ANTENNA PLASMA PROCESSING METHOD ANDAPPARATUS, which is expressly incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to plasma processing with microwave (MW) plasmas,particularly surface wave plasmas (SWP), for example as produced with aRadial Line Slot Antenna, and more particularly, to a method andapparatus providing relatively low electron energies and plasmauniformity near a treated substrate.

BACKGROUND OF THE INVENTION

Typically, during semiconductor processing, a plasma etch process isutilized to remove or etch material along fine lines or within vias orcontacts patterned on a semiconductor substrate. The plasma etch processgenerally involves positioning a semiconductor substrate with anoverlying patterned, protective layer, for example a photoresist layer,into a processing chamber and etching exposed areas of the substratethrough the pattern.

Once the substrate is positioned within the chamber, it is etched byintroducing an ionizable, dissociative gas mixture into the chamber at apre-specified flow rate, while adjusting a vacuum pump to achieve aprocessing pressure. Then, plasma is formed when a portion of the gasspecies is ionized by collisions with energetic electrons. The gas maybe ionized by direct current, radio frequency, microwave energy, orother energy sources known to the art. The energetic electronsdissociate some of the gas species in the gas mixture to create reactantspecies suitable for the exposed-surface etch chemistry. Once the plasmais formed, exposed surfaces of the substrate are etched by the chemistryat a rate that varies as a function of plasma density, average electronenergy, and other factors. The process is adjusted to achieve optimalconditions, including an appropriate concentration of desirable reactantand ion populations to more selectively act upon various desiredfeatures (e.g., trenches, vias, contacts, etc.) in the exposed regionsof substrate. The exposed regions of the substrate where etching isrequired are typically formed of materials such as silicon dioxide(SiO₂), poly-silicon and silicon nitride, for example.

Dissociative attachment, in forming the ions during the exposedsubstrate etch process, prefers electron energy to be as low aspossible. An example is where the chemistry is a Cl2+e− process yieldingCl+Cl−, the negative ions being extracted for etching. Moreover, it ishighly desirable to accomplish this reaction in a spatial afterglowregion of a plasma, to avoid periodic plasma density deficiencies andthe resultant increased risk of damage from unmitigated electromagneticwaves reaching the substrate, for example in microwave plasma sources.

While plasma etching has proven to be generally effective, processefficiency may be negatively impacted by a variety of factors. Forexample, undesirably high average electron energies (T_(e)) tend toimpede ion formation, and thus results in reduced dissociativeattachment at the substrate. Attempts to attenuate the negative effectsnoted above have included the introduction of Multi Pole Magnet (MPM)assemblies, for example as described in U.S. Pat. No. 5,595,627,entitled “Plasma Etching Method” and hereby expressly incorporatedherein by reference. These configurations are not conducive tocorrecting magnetic irregularities by rotating the magnet assembly.Additionally, attempts to improve ion formation at the target substrate,have often necessitated more complex processing chemistries.

Therefore, an apparatus and method for uniformly applying low averageelectron energy plasma etch, to a substrate, is needed.

SUMMARY OF THE INVENTION

In accordance with principles of the present invention, a low averageelectron energy flux onto a substrate in a processing chamber isachieved by providing a cross-B magnetic field in the processing chamberbetween a plasma source and a substrate. The cross-B magnetic fielddirects high energy electrons moving through the plasma process space,leaving electrons arriving in the region near the substrate at anacceptably low ion energy.

In accordance with certain embodiments of the invention, the processingchamber is surrounded with a magnet array that forms a magnetic fieldthrough the chamber that is generally perpendicular to an axial paththrough the chamber from the plasma source, at one end of the chamber,to a substrate support at the other end of the chamber. In accordancewith more particular embodiments of the invention, the field is rotatedabout the central axis of the chamber to enhance azimuthal uniformity ofthe flux onto the wafer.

In certain methods of the present invention, energy from a plasma sourceis imparted into a processing space to generate a plasma at one end of aprocessing chamber. Energetic electrons propagate toward a substratethat is supported at an opposite end of the processing chamber. A dipolemagnetic field is imposed across a process space between the plasmasource and the supported substrate, perpendicular to the direction ofelectron motion, with sufficient strength, height, and position to causeelectrons having energies below an acceptable maximum level to divertfrom the substrate, but to allow electrons having energies at or belowthe acceptable maximum energy to be concentrated onto the substrate. Theprocess may also include the step of reducing electron densitynon-uniformity by rotating the magnetic field coaxially about theprocessing chamber.

In certain embodiments, the dipole magnetic field is applied byutilizing an array of magnets spaced around the exterior of theprocessing chamber. In another embodiment, the array of magnets iscomprised of a collection of magnetic columns. In yet anotherembodiment, the magnetic columns are comprised of a stacked plurality ofdiscrete magnetic elements. In any of the above mentioned embodiments,the field may be applied utilizing permanent magnets.

According to principles of the present invention, a plasma processingapparatus is provided which includes a substrate support at a first end,and an energy source coupled to a second end of the processing chamber.The apparatus is further configured with a Dipole Ring Magnet (DRM)assembly, which envelops the exterior of the processing chamber. The DRMfield is configured to pass perpendicular to, and act upon, the plasmaregion between the energy source and the substrate support, whichresults in filtering the higher energy electrons and allowing lowerenergy electrons to propagate from the plasma source to a quiescentregion near the target substrate. In one embodiment he DRM assembly mayconfigured to rotate coaxially around the processing chamber, serving tosmooth out electron density irregularities.

These and other objectives and advantages of the present invention areset forth in the following detailed description of the drawings inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of one embodiment of the disclosedprocessing system.

FIG. 2 is a top view of the processing chamber and DRM configuration.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

A plasma processing method and apparatus are disclosed in variousembodiments. However, one skilled in the relevant art will recognizethat the various embodiments may be practiced without one or more of thespecific details, or with alternative methods, materials, or components.Well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of various embodiments ofthe invention.

Similarly, for purposes of explanation, specific numbers, materials, andconfigurations are set forth in order to provide a thoroughunderstanding of the invention. Nevertheless, the invention may bepracticed with alternative specific details. Furthermore, the variousembodiments shown in the figures are illustrative representations andare not necessarily drawn to scale.

References throughout this specification to “one embodiment” or “anembodiment” or “certain embodiments” or variations thereof means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe invention, but do not denote that they are present in everyembodiment. Thus, the appearances of the phrases such as “in oneembodiment” or “in an embodiment” or “in certain embodiments” in variousplaces throughout this specification are not necessarily referring tothe same embodiment of the invention. Furthermore, the particularfeatures, structures, materials, or characteristics may be combined inany suitable manner in one or more embodiments.

Nonetheless, it should be appreciated that, contained within thedescription are features which, notwithstanding the inventive nature ofthe general concepts being explained, are also of an inventive nature.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several embodiments orseveral views, FIG. 1 illustrates a plasma processing system 10according to certain embodiments of the invention. The plasma processingsystem 10 may be, for example, a dry plasma etching system or a plasmaenhanced deposition system.

One embodiment of the plasma processing system 10 includes a processingchamber 12 having a chamber wall 14 configured to enclose a processspace 16. The chamber wall 14 is typically a cylinder having a centralaxis 15. The processing chamber 12 has therein a substrate support 18configured to support a substrate 20 in the process space 16.Furthermore, the plasma processing chamber 12 has a plasma source 22coupled to the processing chamber 12 and configured to energize a plasmain the process space 16. During operation of the system 10, thesubstrate 20 is exposed to plasma electrons, or process chemistry, orboth, in process space 16. The plasma source 22 of the system 10 may bea surface-wave plasma (SWP) source that includes a radial line slotantenna 24. The plasma source 22 may be energized by direct current,radio frequency, microwave energy, or other energy sources known to theart. A quartz window 26 may be included to form a sealed interfacebetween the plasma source 22 and the process pace 16. The plasma source22 and the substrate support 18 are coaxially aligned on the chamberaxis 15.

As seen in FIG. 1, the plasma processing system 10 is provided with aplurality of individual magnetic columns 30, which, when combinedtogether, form a dipole ring magnet (DRM) as illustrated further in FIG.2. The magnetic columns 30 are situated coaxially outward from thechamber wall 14, and run substantially parallel with the chamber wall 14and parallel to adjacent magnetic columns 30. To cooperate with theother magnetic columns 30 to form a DRM, each magnetic column 30 isrotated incrementally about its axis, which is parallel to the axis 15of the chamber 12, such that the magnetic forces of each individualmagnetic column 30 combine to result in an overall dipole magnetic field44. In one embodiment, the field lines pass generally from thenorthernmost point of the dipole ring, to the southernmost portion ofthe dipole ring. The rotations of the magnets are related such that thelines of the B-field of the DRM through the processing space 16 in thechamber are parallel and perpendicular to the chamber axis 15.

In use, the magnetic columns 30 are positioned and dimensioned to allowthe resulting magnetic field lines to act perpendicularly upon someportion of the process space 16. The columns originate at a firstdistance 32 below the quartz window 26, and extend to a second distance34 below the quartz window 26. In one embodiment, the first distanceoriginates where the plasma is no longer exothermic. The length of eachmagnetic column 30 should be dimensioned so that it is long enough toachieve electron cooling and low energy selection, and short enough tominimize plasma density loss. If the wafer is radio frequency (RF)biased, the magnetic columns 30 could be well above the substrate 20 tominimize DRM RF heating. Alternatively, terminal ends of the magneticcolumns 30 could be placed in close proximity to the substrate 20 totake advantage of the DRM RF plasma. In one embodiment, the magneticcolumns 30 originate at a first distance 32 of approximately 10 cm belowthe quartz and extend to a second distance 34 of approximately 45 cmbelow the quartz window 26. In one exemplary configuration, thesubstrate 20 could be placed coincident with the plane formed by theterminal ends of the magnetic columns 30 to eliminate DRM RF plasmaeffects.

In use, a plasma source 22 is energized to generate a plasma within theprocess space 16, which forms at the end of the chamber adjacent thewindow 26 and propagates toward the substrate support 18 into the plasmaspace 16. The Radial Line Slot Antenna 24, coupled to a microwavesource, may be used to form a surface wave plasma. Details of the RadialLine Slot Antenna 24 in an SWP source are described in U.S. Pat. No.8,114,245, hereby expressly incorporated herein by reference. In theplasma, if left unchecked, a majority of the produced electrons areexcessively energetic, which results in unacceptably low negative ionconcentrations in the region near the substrate 20. This can result inpoor performance of the plasma etch upon the substrate. However, byintroducing the magnetic columns 30, the resulting DRM fieldadvantageously influences the distribution of electron energy levelsnear the substrate 20.

As high energy electrons travel from the top of the process space 16 tothe substrate 20, the most energetic electrons are highly influenced bythe DRM field and are deflected away from the substrate 20 with a forceperpendicular to their direction of travel. Conversely, lower energyelectrons are less significantly impacted by the DRM magnetic fieldforces, and are permitted to propagate further downward into the chambertoward the substrate 20. The presence of the DRM field results in anelectron energy gradient 36, wherein less desirable high energy electronconcentrations reside at the top of the process space 16, or aredirected into the chamber wall 14 where they are sent to groundpotential. Conversely, lower energy electrons propagate into a quiescentregion 38 near the substrate 20, where their reduced energy facilitatesnegative ion production and effective etch performance.

FIG. 2 is a top view of the plasma processing system 10. The pluralityof magnetic columns 30 cooperate to form a dipole ring magnet (DRM) 40,which surrounds the chamber wall 14. Each of the magnetic columns 30 areimmovably mounted with a degree of incremental rotation so that thecolumn field lines 42 cooperate to produce the desired collection of DRMfield lines 44. For clarity of discussion, the resultant magnetic fieldof the DRM 40 can be described as having a north, east, south and westpole. The resulting DRM field lines 44 can be arbitrarily directed byorienting two opposite magnetic columns 30N and 30S so that their columnfield lines 42 are coincident with the center of the process space 16.

By way of example in FIG. 2, the northernmost magnet column 30N andsouthernmost column 30S, are positioned so that their respective columnfield lines 42 are oriented due south and pass through the center of thesubstrate support 18. To further cooperate with those two selectedmagnetic columns 30N, 30S, the easternmost magnetic columns 30E andwesternmost column 30W are positioned so that their respective columnfield lines 42 are oriented due north. Magnetic columns 30 i subtendingthe arc between the aforementioned four magnetic columns 30N, 30S, 30E,30W, are progressively rotated by a fixed angular measurement. Thisangular positioning is determined by 180/(n+1), where n equals thenumber of magnetic columns 30 positioned between adjacent “compass”poles. For example, in FIG. 2, there are five magnetic columnspositioned between the northernmost and easternmost magnetic columns 30.Therefore, each magnetic column 30 is rotated thirty degrees as theyprogress around the perimeter of the chamber wall 14, although theserotations may be modified to maintain parallel field lines in thechamber or to obtain some other field shape, if desired. Necessarily,diametrically opposed magnetic columns 30 have column field lines 42oriented in the same direction. For example, in a proper configuration,the northeast and southwest magnetic columns 30 have column field lines42 oriented in the same direction.

Overall, what results, are DRM field lines 44 which are orientedhorizontally with respect to the target substrate, and passperpendicular to the direction of electron travel. While other ringmagnetic assemblies are known to the art of plasma etch processing, theyare often implemented in a multi-pole configuration. For example,adjacent columns may have alternating poles facing the center of thesubstrate 20, configured to direct electron densities away from thechamber wall 14. However, a multi-pole magnet disadvantageouslypossesses a strong radial gradient and azimuthal field symmetry. The DRM40 of the disclosed invention, however, aims to beneficially concentratelow energy electrons near the substrate 20 being processed whilemaintaining a high degree of uniformity. Because of the DRM 40 improvedradial uniformity, the entire DRM 40 may be coaxially rotated withrespect to the substrate 20 and chamber wall 14, to diminish anyelectron concentration irregularities that may exist.

Although only certain embodiments of this invention have been describedin detail above, those skilled in the art will readily appreciate thatmany modifications are possible in the embodiments without materiallydeparting from the novel teachings and advantages of this invention.Accordingly, all such modifications are intended to be included withinthe scope of this invention.

What is claimed is:
 1. A method of obtaining a low average electronenergy flux onto a substrate in a processing chamber, comprising:supporting a substrate for processing at a first end of a processingchamber with a surface of the substrate facing a processing space in theprocessing chamber that contains a processing gas; coupling energy intothe processing space to form a plasma containing ions of the processinggas at a second end of the chamber opposite the substrate; positioning aplurality of magnetic columns coaxially outward from a chamber wall andparallel to the chamber wall, wherein each magnetic column originates afirst distance spaced from the second end of the processing chamberwherein the plasma in the processing chamber is no longer exothermic;allowing electrons to propagate in a direction from the second end ofthe processing chamber toward the substrate at the first end of theprocessing chamber; applying a dipole magnetic field, transverselyacross the chamber and perpendicular to the direction of propagation ofthe electrons, along a portion of the processing space, wherein theposition of the dipole magnetic field is established based on the firstdistance and extending a length of the plurality of magnetic columnsfrom the origination of the magnetic columns toward the first end of theprocessing chamber; and filtering the electrons with the dipole magneticfield to divert electrons that have an energy level above an acceptablemaximum level from the substrate and allowing electrons that have anenergy level at or below the acceptable maximum level to treat thesubstrate.
 2. The method of claim 1, wherein the portion of theprocessing space along which the dipole magnetic field is appliedextends sufficiently from the first distance origination of theprocessing space portion toward a second distance from the second end ofthe processing space and toward the substrate to allow for electroncooling and low energy selection and terminates a distance from thesubstrate so as to minimize plasma density loss.
 3. The method of claim1 further comprising rotating the dipole magnetic field.
 4. The methodof claim 1 wherein the energy is microwave energy.
 5. The method ofclaim 4 wherein the coupling of the microwave energy into the processingspace is from a Radial Line Slot Antenna at the second end of theprocessing chamber.
 6. The method of claim 1, wherein: the portion ofthe processing space along which the dipole magnetic field is appliedoriginates at the first distance spaced from the second end of theprocessing chamber wherein the plasma is no longer exothermic andextends sufficiently from the first distance origination of theprocessing space portion toward the substrate to allow for electroncooling and low energy selection and terminates a distance from thesubstrate so as to minimize plasma density loss; the applying of thedipole magnetic field includes rotating the dipole magnetic field aboutan axis extending through the center of the processing chamber in thedirection; and the coupling of energy into the processing space includescoupling microwave energy into the processing space from a Radial LineSlot Antenna at the second end of the processing chamber.